Apparatus and method for treating venous reflux

ABSTRACT

Disclosed is an ablation method and apparatus used to close veins for treatment of venous insufficiency disease. The apparatus includes a catheter proportioned for insertion into a vein, a pair of inflatable balloons spaced apart on the catheter body, and an ablation electrode array disposed between the balloons. According to the disclosed method, the catheter is introduced into the vein to be treated and the balloons are distended. Blood is flushed and aspirated from the site between the balloons. RF power is applied to the electrode array, causing scarring of the vessel walls and eventual sealing of the vein.

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/261,321, filed Jan. 16, 2001.

FIELD OF THE INVENTION

[0002] The present invention relates generally to the field ofapparatuses and methods for treating body tissue, and specifically toapparatuses and methods for treating interior surfaces of blood vessels.

BACKGROUND OF THE DISCLOSURE

[0003] Veins of the lower extremities are equipped with a series ofone-way bicuspid valves that pulse open and closed. These valvesfacilitate flow of venous blood towards the heart and prevent venousblood from flowing away from the heart. In a condition known as venousinsufficiency, defective valves do not close properly, resulting invenous reflux (backward flow of blood within the veins). Venous refluxcan result in pooling of blood within the veins, and can lead to pain,swelling, ulcers, and varicose veins.

[0004] Venous reflux disease (VRD) most commonly occurs in the saphenousvein. Current treatments for VRD involve re-routing of blood from theaffected vein into the nearby vasculature. In one such treatment, knownas venous stripping, the long and/or short saphenous vein is removed.Another treatment for VRD involves suture ligation of the long and/orshort saphenous vein. More recently other methods have been developed,including the application of RF energy to the interior of the vein, butthe method is slow, requiring 30 minutes to an hour to perform, and istedious for the physician to perform since it requires a constant, slowwithdrawal of the device from the vein during the application of energy.These detriments make it impractical to perform in the clinic.

SUMMARY OF THE INVENTION

[0005] The present invention is an ablation method and apparatus used toclose veins. An apparatus according to the present invention includes acatheter proportioned for insertion into a vein, a pair of inflatableballoons spaced apart on the catheter body, and an ablation electrodearray disposed between the balloons. According to the disclosed method,the catheter is introduced into the vein to be treated and the balloonsare distended. Blood is flushed and aspirated from the site between theballoons. RF power is applied to the electrode array, causing scarringof the vessel walls and eventual sealing of the vein. A pressure bandagemay be applied around the patient's leg post-operatively for a shorttime to facilitate scarring and sealing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1A is a side elevation view of an ablation catheter fortreatment of venous reflux disease;

[0007]FIG. 1B is a cross-sectional side view of the catheter of FIG. 1A,taken along the plane designated 1B-1B in FIG. 1A.

[0008]FIG. 2 is a block diagram of an ablation system utilizing thecatheter of FIG. 1A;

DETAILED DESCRIPTION

[0009] Referring to FIGS. 1A and 1B, an ablation catheter 10 includes acatheter body 12, which is preferably an extrusion formed of a flexiblepolymeric material suitable for surgical use. Body 12 preferablyincludes three fluid lumens 14, 16, 18, of which lumens 16 and 18 areopen to one another at the distal region of the catheter body 12. Acentral guidewire lumen 19 extends from the proximal end to the distalend of the catheter and receives a guidewire 21.

[0010] A pair of spaced-apart balloons 20 is disposed on the catheterbody 12. The balloons are formed of an elastic or inelastic material.Each balloon is fluidly coupled to lumen 14 via small inflation openings22 formed in the body 12. The proximal end of the lumen 14 terminates atan inflation port 24 that couples to a source of inflation medium forinflation and deflation of the balloons 20. The balloons are preferablysealed against the catheter body 12 such that when they are inflatedthey do not leak inflation medium directly into the vein. Lumen 14itself is collapsible when a vacuum is applied to it.

[0011] An electrode array 26 is positioned on the catheter body 12between the balloons 20. The array 26 includes one or more bipolarelectrode pairs 28 preferably formed over the circumference of thecatheter body. In a preferred configuration, the array extends along asufficient length of catheter to permit simultaneous ablation of thefull length of the targeted region of the vein. This avoids the need forrepositioning the catheter within the vein, or for dragging theenergized electrode through the vein to ablate the desired length of thevessel.

[0012] The electrodes preferably are constructed of a thin layer depositusing a conductive metal, for instance silver or gold. In anotherpreferred embodiment the electrodes are constructed of a fine elasticconductive mesh with integrated insulating and conducting regions. Anelectrode mesh of this type is utilized on the NovaSure® EndometrialAblation System sold by Novacept, Inc. of Palo Alto, Calif.

[0013] Insulated electrode leads (not shown) extend from the electrodepairs and through the catheter body 12, and are coupled to a cable 42that interfaces with a RF controller 44 (FIG. 2). Preferably, the RFcontroller 44 includes RF circuitry 45 having both low and highimpedance transformation circuits, and automatically selects theimpedance circuit based on real time measured impedance of the ablationelectrode in contact with the vessel tissue. An impedance-matched RFgenerator system of this type is described in International ApplicationNo. PCT/US99/09904, Filed May 7, 1999, and entitled A RADIO-FREQUENCYGENERATOR FOR POWERING AN ABLATION DEVICE, the entirety of which isincorporated herein by reference. An RF controller employing suchimpedance-matching technology for ablation applications is the NovaSure®RF Controller sold by Novacept, Inc. of Palo Alto, Calif.

[0014] The center-to-center spacing C between the electrodes (i.e. thedistance between the centers of adjacent electrodes), the distancebetween the electrodes, and the widths of the electrodes are selected sothat ablation will reach predetermined depths within the tissue,particularly when controlled power is delivered through the electrodes(where power density is the power delivered per unit surface area atwhich low impedance, low voltage ablation can be achieved).

[0015] The depth of ablation is also affected by the electrode density(i.e., the percentage of the target tissue area which is in contact withactive electrode surfaces) and may be regulated by pre-selecting theamount of this active electrode coverage. For example, the depth ofablation is much greater when the active electrode surface covers morethan 10% of the target tissue than it is when the active electrodesurfaces covers 1% of the target tissue.

[0016] Although the electrodes shown in the drawings are arranged in aparticular pattern, it should be appreciated that the electrodes may bearranged in any pattern that will result in ablation to desired depths.

[0017] In one embodiment, the electrode spacing is approximately 0.5-1.0mm with the active electrode surfaces covering approximately 10% of thetarget region. Delivery of approximately 8-10 watts of power percentimeter squared of tissue surface area using this electrodeconfiguration will achieve ablation to a depth of approximately 0.1-2.5mm. After reaching this ablation depth, the impedance of the tissue willbecome so great that ablation will self-terminate as described withrespect to the operation of the system.

[0018] The proximal end of lumen 18 bifurcates into two sections oftubing 34, 36. First section 34 terminates at a vacuum relief valve 38that regulates the vacuum level within the catheter. Second section 36terminates at a flush port 40 that is connectable to a source of salineor other fluid that may be injected into the vein via perforations 30.Flush port 40 may also be coupled to a vacuum monitoring circuit 48,which detects the pressure within the lumen 16, 18 so as to monitor toamount of vacuum applied. In one embodiment, the vacuum pump 46 andvacuum monitoring circuit 48 may be housed within the RF controller 44,as shown in FIG. 2.

[0019] A plurality of pores/perforations 30 is formed in the catheterbody 12, between balloons 20 as shown. If the array is formed of a mesh,the perforations may be the interstices of the mesh. The perforationsare fluidly coupled to fluid lumens 16, 18—which may be contiguous withone other at the distal portion of the catheter body. The proximal endof lumen 16 terminates at a suction port 32 that is connectable to avacuum pump 46. Thus, application of a vacuum to lumen 16 draws moistureand fluid through the perforations 30, through lumen 16 of the catheterbody 12 and out the proximal end of the catheter body. The vacuum signalis transmitted up lumen 18, through connection 40, to the pressuretransducer in the vacuum monitoring circuit 48 in the RF Controller. Thevacuum monitoring circuit assures the target tissue is under theappropriate vacuum limits at appropriate times throughout the procedure.Application of a vacuum also facilitates electrode-tissue contact bydrawing tissue into contact with the electrodes.

[0020] One preferred method of using the ablation catheter 10 will nextbe described. First, an incision is made to expose the vessel to betreated. For the saphenous vein or long saphenous vein, the incision isformed in the patient's groin. Guidewire 21 is inserted into the veinand the catheter is advanced over the guidewire 21 into the desiredposition within the vein. Balloons 20, 22 are inflated into contact withthe interior wall of the vein, using an inflation medium introducedthrough port 24 and lumen 14. A flushing medium, preferably saline, isdirected into flush port 40 and exits the catheter via perforations 30where it functions to flush the region of the vessel between theballoons. It may be desirable to initiate this flow of saline prior to,or simultaneously with, insertion of the catheter to prevent blood fromclogging pores/perforations 30. Suction is applied via vacuum port 32 toaspirate the mixture of saline and blood from the vein, throughperforations 30 and out of the catheter. The suction in this step ispreferably insufficient to collapse the vein. Flushing and aspirationare continued until much of the blood is removed from the vein, althoughsome blood may remain in the vein without impairing operation of thecatheter. A slight positive pressure, sufficient to overcome venouspressure, is maintained on the system after the flushing process iscomplete in order to maintain patency in perforations 30 and lumens 16and 18.

[0021] Next, the RF controller 44 energizes the electrode array 26 todeliver ablation energy to the surrounding tissue. Suction is preferablyapplied to the vacuum port 32 during ablation for two reasons. First,suction collapses the vessel, thus drawing the interior wall of thevessel into contact with the electrode array. Second, suction drawsmoisture (gas and vapor) away from the ablation site. Moisture build-upat the ablation site may be detrimental in that it provides a conductivelayer that carries current from the electrodes even when ablation hasreached the desired depth. This undesirable continued current flow heatsthe moisture and surrounding tissue, and thus causes ablation tocontinue by unpredictable thermal conduction means.

[0022] Ablation causes tissue to dehydrate and thus to decrease inconductivity. By applying a vacuum or otherwise shunting moisture awayfrom the ablation site, and thus preventing liquid build-up, there is noliquid conductor at the ablation area during use of the ablation deviceof the present invention. Thus, when ablation has reached the desireddepth, the impedance at the tissue surface becomes sufficiently high tostop or nearly stop the flow of current into the tissue. RF ablationthereby stops and thermal ablation does not occur in significantamounts. If the RF controller is equipped with an impedance monitor, aphysician utilizing the ablation device can monitor the impedance at theelectrodes and will know that ablation has self-terminated once theimpedance rises to a certain level. Alternatively the impedance monitormay automatically shut down power delivery after the desired impedancehas been reached, and display a message or signal a type of indicator tonotify the physician that the procedure is complete. By contrast, in theabsence of moisture removal, the presence of liquid around the bipolarelectrodes would cause the impedance monitor to give a low impedancereading regardless of the depth of ablation which had already beencarried out, since current would continue to travel through thelow-impedance liquid layer.

[0023] Collagen and elastin in the vessel wall may shrink during powerapplication, collapsing the vessel down onto the catheter. Once ablationhas self-terminated and/or ablation has been performed to the desireddepth, delivery of RF energy to the electrodes is terminated. Relievingthe pressure at connector 24 deflates balloons 20. Applying a vacuum toconnector 24 then collapses lumen 14, reducing the size of the catheterto facilitate removal. The catheter is then removed from the vein. Acompression bandage is applied to patient over the site of the ablation,so as to hold opposing portions of the ablated vessel in contact withone another. This causes the ablated portions of the vessel to sealagainst one another, thus closing the vessel and causing blood flow bediverted to surround vessels.

We claim:
 1. A method of sealing a blood vessel, comprising the stepsof: providing a catheter including an elongate body, a pair ofinflatable balloon members on the elongate body, and an electrode arrayon the elongate body between the balloons; positioning the catheterwithin a blood vessel; inflating the balloon members into contact withan interior wall of the blood vessel; flushing blood from the portion ofthe blood vessel extending between the inflated balloon members;energizing the electrode array to cause ablation of the interior wall ofthe blood vessel; removing the catheter from the blood vessel; andcompressing the blood vessel, causing opposed ablated regions of theinterior wall to seal against one another.
 2. The method of claim 1wherein a vacuum is applied to the portion of the blood vessel extendingbetween inflated balloon members during ablation, said vacuum collapsingthe vessel, thereby drawing the interior wall into contact with theelectrode array.
 3. The method of claim 2 wherein the catheter elongatebody includes a plurality of openings, and wherein the vacuum is appliedthrough the openings.
 4. The method of claim 1 wherein a vacuum isapplied to the portion of the blood vessel extending between inflatedballoon members during ablation, said vacuum drawing moisture generatedduring ablation away from the tissue.
 5. The method of claim 4 whereinthe catheter elongate body includes a plurality of openings, and whereinthe vacuum is applied through the openings.
 6. The method of claim 1,wherein the flushing step includes flushing the portion of the bloodvessel extending between the balloon members with saline, and aspiratingblood and saline from the said portion of the blood vessel.
 7. Themethod of claim 1, wherein the catheter elongate body includes aplurality of openings, and wherein the aspirating step includes applyinga vacuum to the catheter to aspirate the blood out of the vessel throughthe openings.
 8. The method of claim 1 wherein the electrode array is abipolar array.
 9. The method of claim 1 wherein the method furtherincludes the steps of, prior to energizing the electrode array to causeablation: positioning the electrode array in contact with the interiorwall of the blood vessel and measuring impedance of the tissue incontact with the electrode array; and automatically selecting between alow impedance transformation circuit and a high impedance transformationcircuit based on the impedance of the tissue in contact with theelectrode array.
 10. The method of claim 9 wherein the step of measuringthe impedance of the tissue in contact with the electrode array includesproviding a low-power RF signal to the electrode array.
 11. The methodof claim 9 wherein the step of selecting includes selecting thetransformation circuit having an impedance closest to the measuredimpedance of the tissue in contact with the electrode array.
 12. Themethod of claim 1 wherein the energizing step causes flow of currentinto the tissue, and wherein the method further includes the step ofcausing automatic termination of current flow into the interior wallonce a selected ablation depth has been approximately reached.
 13. Themethod of claim 12 wherein said termination occurs regardless of whetherthe electrode array continues to be energized.
 14. The method of claim 1wherein the removing step includes the step of collapsing the catheterinto a reduced diameter step and withdrawing the collapsed catheter fromthe vessel.
 15. The method of claim 14 wherein the collapsing stepincludes the step of applying a vacuum to a lumen in the catheter.
 16. Adevice for sealing a blood vessel, comprising: a catheter having anelongate body positionable within a blood vessel; a pair of inflatableballoon members on the elongate body, the balloon members expandableinto contact with an interior wall of the blood vessel; an electrodearray on the elongate body between the balloons; at least one opening inthe elongate body, between the balloons; a source of flushing fluidcoupled to the opening; a vacuum source fluidly coupled to the opening,the vacuum source providing sufficient vacuum pressure to aspirate bloodand flushing fluid out of the blood vessel through the opening; and asource of ablation energy electrically coupled to the electrode arraysuch that energization of the electrode array causes ablation of bloodvessel tissue in contact with the electrode array.
 17. The device ofclaim 16 wherein the vacuum source is further operable to draw theinterior wall of the blood vessel into contact with the electrode array.18. The device of claim 16 wherein the vacuum source is further operableto draw moisture generated during ablation away from the tissue and intothe elongate body.
 19. The device of claim 16 wherein the at least oneopening comprises a plurality of openings in the elongate body.
 20. Thedevice of claim 16 wherein the electrode array is a bipolar array. 21.The device of claim 16 wherein the source of ablation energy includes anRF generator having a low impedance transformation circuit and a highimpedance transformation circuit, an impedance detection circuit formeasuring impedance of tissue in contact with the electrode array, and acontrol circuit for automatically selecting between the low impedancetransformation circuit and the high impedance transformation circuitbased on the impedance of the tissue in contact with the electrodearray.
 22. The device of claim 21 wherein the control circuit is forselecting the transformation circuit having an impedance closest to themeasured impedance of the tissue in contact with the electrode array.